As an architectural historian, William Curtis is well known for his monographs on Le Corbusier and Denys Lasdun, and for his Modern Architecture Since 1900 - certainly the best single overview of 20th-century architecture, linking as it does a series of astute analyses of specific buildings and architects to a strong central argument. If it's a surprise to find an exhibition of his photographs - some 100 of them - filling all the galleries at Toulouse's architecture centre, its content, reinforced by the installation, is readily explicable in the light of his major books.

At one point in Modern Architecture, Curtis notes how architects like Wright, Le Corbusier and Kahn 'drew upon several cultures and traditions in formulating their respective versions of a modern architecture'. Of the greatest 20th-century buildings, he says: 'To slot them into the modern movement is to miss much of their value for they are also relatives of past works of excellence.' This show, ranging far in space and time in its choice of subjects, brings the past to bear on the present in provocative ways.

The photographs are placed directly on the wall, unframed, which adds to their immediacy. Chronology is deliberately scrambled, while the same building (Ronchamp, for instance) may appear in different contexts.

Some juxtapositions have a precedent: the Cistercian monastery of Le Thoronet next to Corb's La Tourette, or his Chandigarh Assembly building beside the Jantar Mantar observatory in Jaipur - in each case a source acknowledged by the architect. Others are less expected.

There's a lovely pairing of Siza's Leça de Palmeira swimming pool with the pool at the 7th-century temple complex of Badami in southern India. This is inhabited architecture, though the accent is on leisure in the one and laundry in the other. Buildings in use recur, but more often Curtis tends to underscore the abstraction implicit in his subjects.

With a group of photos that includes the oculus of the Pantheon, the crescent window of Utzon's Can Lis, and Ronchamp as a mysterious cave, dates and names are effectively abolished, and in their place comes a cosmic dimension to architecture, an essence - enclosure pierced by light.

Curtis' viewpoint flattens Fallingwater, so that it reads as a series of strata.

Whether man-made - as at the Parthenon, Epidaurus, or Uxmal - or natural - as in the mountains behind a Moroccan village and oasis - Curtis draws attention to such strata (steps, platforms, etc) as if recording the modulation of landscape into building - a process of abstraction again, as geology becomes geometry.

The show would profit from a little trimming. A few shots are inconsequential. One of an American diner might have strayed from a William Eggleston exhibition (though it lacks his saturated colour). The campanile of San Marco, Venice, is paired with the Chrysler Building, the World Trade Center with the twin-towered New Mexican church of San Esteban del Rey;

but unless Curtis intends some point about commerce supplanting Christendom, the connections between them are superficial (just a visual rhyme), while the New York buildings jeopardise the 20th-century segment of the show, being inferior in quality to his other examples.

But at this point the end wall of the gallery is also in sight, with five large images upon it.

At the centre, surging to the horizon, is the Salk Institute's long rill; on either side are the Robie House and Lake Shore Apartments (in an unusual worm's-eye view); and flanking them are the Governor's Palace at Uxmal and the Parthenon. Wright, Mies and Kahn keep elevated company here, but the ensemble is completely convincing.

It's a reminder that few professional photographers of architecture in recent years have ranged as widely as Curtis. Ezra Stoller specialised in post-war American Modernism, while Julius Shulman glamorised its West Coast variants; only G E Kidder Smith looked as keenly at the past as at the 20th century.

Two small, attractive pamphlets accompany the show, but it has ample material for a book; the images linked, perhaps, by extracts from three lectures Curtis is giving at Toulouse before the exhibition ends. But the show itself deserves more than a professional audience. It's of a kind that could reach a larger public, sparking interest in architecture of all eras.

The centre is open from Mondays to Saturdays, 1pm-7pm. Website: http: //cmav. free. fr

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